MOMBASA - Armed raiders killed 12 villagers and set fire to houses in Kenya's Coastal region, police and the Red Cross said on Friday, in a revenge attack that is part of a long-running dispute over grazing land and water.

The attackers targeted a village in the Tana Delta inhabited by Pokomo farmers late on Thursday, less than three weeks after 100 Pokomo tribesmen armed with spears and machetes attacked an Orma settlement and killed more than 50 people.

The violence follows deadly riots in the main coastal port of Mombasa after the assassination of a radical Muslim cleric.

While the two events are unrelated they have exposed deep social, political and sectarian divides that could lead to more violence ahead of a presidential election next year.

"They attacked our people and killed so many of our people, burnt our houses and left us with a lot of pain. Did you expect we would let them get away it?" said 29-year-old Ali Dorobo, an Orma from the area.

Dorobo said some in his community were not satisfied with the scale of their attack, suggesting the violence could escalate.

"We know they will organise another attack and we are waiting. This will not end soon," Dorobo told Reuters by telephone.

Settled Pokomo farmers and semi-nomadic Orma pastoralists have clashed intermittently for years over access to grazing, farmland and water.

The bad blood re-ignited late last month after the Pokomo accused the pastoralists of grazing cattle on their land.

BURNING AND SHOOTING

Efforts by top government officials - among them Prime Minister Raila Odinga who visited the area after the previous attack - to defuse the tensions have so far failed.

Jillo Dabacha, who chairs a community security group in the Tana Delta locality, said gunfire broke out last night and continued until dawn. He said the attackers appeared well organised.

"They surrounded the Pokomo village and attacked, burning houses and shooting indiscriminately," Dabacha said. A number of women and children had fled the village and were likely hiding in the surrounding bush, he said.

Mwanaisha Hamisi, head of the Kenyan Red Cross in Coastal province, told Reuters its staff had been ferrying the injured to hospital since the early morning.

"The bodies have either gunshot wounds or burns, or both," he said.

Cattle rustling and clashes over grazing and farming land are relatively common between communities in arid areas of east Africa and often escalate into revenge attacks.

Such attacks have become increasingly violent in recent years because of a steady influx of weapons across Kenya's porous borders, in particular from war-ravaged Somalia.